The S511 is an OK ssd. Personally on a 3-4k build I would be looking at 240GB Intel 520, Corsair Force GS 240GB, SanDisk Extreme 240 or maybe even a Vertex 4 512GB drive. Anything less than 240GB will be slower.

I agree with the 120GB SSD, but my reasoning would be more for the size of the storage. While, 120GB IS quite a lot, after installing Windows and 4 or 5 large games, I'm down to about 30GB remaining. This isn't a big deal for me, since I have a relatively quick WD Black as a secondary drive. YOU, however, are putting in a 3TB GREEN Drive which, while perfectly fine for storage, will be quite slow to run any software from. By getting a min. 240GB SSD, you'll be effectively eliminating any 'range anxiety' you may suffer from having too small of a drive.

Plus 240Gb SSD's are quite a bit cheaper than they used to be. You can get a Crucial M4 256GB for $200...